1. Field of the Invention
This invention relates to a sound-absorbing structure in a vehicular compartment.
2. Description of the Prior Art
FIGS. 6 and 7 illustrate a prior art sound-absorbing structure built into the roof of an automotive vehicle. This structure comprises a roof panel 1 and a molded head lining 2 made of an acoustic material and separate from the roof panel 1. The roof panel 1 and the head lining 2 lie parallel, leaving an air chamber 3 therebetween. As shown in FIG. 7, the head lining 2 comprises a substrate 4 made of corrugated cardboard or a gas-permeable material, and a nonwoven fabric 5 covering the inner surface of the substrate 4 (See Automotive Engineering Manual, section 6, issued by SOCIETY AUTOMOTIVE ENGINEERS OF JAPAN INCORPORATION). In this sound-absorbing structure, the air chamber 3 enhances the acoustical properties of the head lining 2 so as to keep the passenger compartment quiet.
However, since the air in the passenger compartment leaks out of the vehicle through the head lining 2 and the air chamber 3 due to the negative pressure developed by movement of the vehicle, the head lining 2 consequently acts as an air filter and thus collects dust from within the passenger compartment. The dust dirties the outer surface of the head lining 2 and degrades the appearance of the head lining 2.